A well known application for Y-tools is the mounting of an electric submersible pump in a well bore or production tubing. The pump is mounted on the lower end of the main limb of the Y-tool and the by-pass limb provides a pathway for access below the pump to well tools and logging tools into the well. By passing such tools through the by-pass limb of the Y-tool, the electric submersible pump does not have to be recovered from the well before such an operation is carried out. Generally, the bypass limb of the Y-tool will descend further into the well bore than the main limb in order to ensure that well tools and logging tools passing through the by-pass limb, exit the by-pass limb beneath the electric submersible pump. These tools can then continue down into the well below the pump.
While the by-pass limb of the Y-tool provides a convenient path through the well beneath the electric submersible pump, while the pump is operating, the by-pass limb is generally closed off to fluid flow thereby forcing fluid flow up the main limb of the Y-tool.
Blanking plugs are known for insertion into the by-pass limb during operation of the electric submersible pump. However, such blanking plugs must be recovered via a wirelining operation each time access is required through the by-pass limb and therefore automatic pressure operated valves have been used to selectively open and close the by-pass limb of a Y-tool.
A known blanking tool is described in GB 2 327 961 in which a flapper valve is pivotally mounted between the two limbs of the Y-tool and can take up a position wherein one or other limb is closed or, in the absence of fluid flow, a position wherein both limbs are open to allow for access for logging tools to the well via the by-pass limb.
The flapper valve is provided with sealing means on the upper and lower faces. When one of the limbs of the Y-tool is closed off, the flapper valve adopts a position over that limb. Sealing means may also be provided on around the upper edge of the limbs such that closure of the flapper valve over one of the limbs seals that limb against fluid flow.
However, the flapper valves which are used are susceptible to wear and tear over time and the upper and lower surfaces of the flapper valve can become warped which prevents the valve from maintaining an effective seal within the valve seats at the top of each limb of the Y-tool. If the flapper valve is unable to provide an effective seal across either or both of the limbs of the Y-tool, the required pressure differential will not be established across the valve and the valve will effectively take up an open position between the two limbs of the Y-tool at all times.
Replacement of the flapper valve requires recovery of the Y-tool from the well leading to a length and costly shut down operation.